The present invention relates to a heat resistant phosphorus-containing polymeric flame retardant and process for preparing the same.
Flame-retardant polymeric materials can be obtained by copolymerizing flame retardants into polymer molecular structures, or by blending polymers with flame retardants. By using copolymerization method, although permanent flame retardancy is obtainable, other physical properties of the polymeric materials are degraded and the manufacturing cost is high. A blending method has the advantages of easy processing and low manufacturing cost. Moreover, other additives such as thermal stabilizers and antistatic agents can also be blended with the polymeric materials. However, the flame retardants easily migrate to the surface of the fabricated products and then disappear, thus the flame retardancy is short-lived. Moreover, due to the poor compatability of flame retardants with polymeric materials and poor dispersity, when the amount of flame retardants to be added is large, their physical properties of the resulting polymeric materials are often deteriorated.
Although known phosphate flame retardants contain high content of phosphorus, their molecular weight is generally less than 2000, and thus have poor heat resistance. Their thermal decomposition temperature (T.sub.d) is lower than 300.degree. C., and the weight loss (280.degree. C., 3 min, under N.sub.2) is larger than 1%. Thus this kind of flame retardant is not suitable for being processed at an elevated temperature. Phosphorus-containing polyesters having a molecular weight larger than 30,000 can be made, however, as phosphorus will inhibit the esterification and condensation reactions, unsually, the phosphorus content thereof is less than 1%. This phosphorus-containing polyester can only be used directly, and is not suitable for adding to other polymeric materials as a flame retardant.